<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div id="app1">
    <my-header></my-header>
    <my-footer></my-footer>
</div>
<div id="app2">
    <my-header></my-header>
</div>
<script src="js/vue.js"></script>
<script>
let vm1=new Vue({
   el:"#app1",
   components:{
       "my-header":{template:`<h1>Hello Header</h1>`},
       "my-footer":{template:`<h1>Hello Footer</h1>`}
   }
 });

let vm2=new Vue({
    el:"#app2"
});
</script>
</body>
</html>